1. Field of the Invention
The present invention relates to an optical fiber reinforcing method and an optical fiber reinforcing device reinforcing a fusion splicing point of optical fibers and particularly to an optical fiber reinforcing method and an optical fiber reinforcing device to improve the reinforcing operation of optical fibers.
2. Description of the Related Art
FIGS. 1A to 1C show a related art fusion splicing device, a related art reinforcing device, and a heat shrinkable reinforcing sleeve used in the related art reinforcing device.
With reference to FIG. 1A, the related art fusion splicing device 1 is a device for melting and splicing end faces of a pair of optical fibers 3, 3 by means of arc discharge generated by a pair of discharge electrode rods 14, 14 positioned at a mid point C1 of the fusion splicing device 1. Meanwhile, a part of a sheath portion is previously removed from each optical fiber 3, and the end faces of the optical fibers 3, 3 are cut with a special tool, such as a cleaver or the like to obtain a flat end face.
The related art fusion splicing device 1 is generally comprised of an optical fiber holder 11 to hold sheath portions of the pair of optical fibers 3, 3, a V-groove 12 to guide each optical fiber 3 from which the sheath portions have been removed are fixed, and the pair of discharge electrode rods 14, 14 for carrying out arc discharge.
Although the fusion splicing device 1 shown in FIG. 1A integrally has a heating and reinforcing device 2, the fusion splicing device 1 and the heating and reinforcing device 2 may be formed as separate bodies.
Generally, the strength of a fusion spliced optical fiber is weak at a fusion splicing point M thereof. Therefore, in general, the fusion spliced optical fiber 3 is reinforced with a reinforcing member, such as a heat shrinkable reinforcing sleeve, for protecting and reinforcing the fusion splicing point M.
With reference to FIG. 1C, a heat shrinkable reinforcing sleeve 13 is generally comprised of an outer-tube 131 which shrinks when heated, an inner-tube 132 which is melted by heat of a heater (not shown here), a strength member 134 made of metal or the like, and a fusible hot-melt 133 filling inside the outer-tube 131. The heat shrinkable reinforcing sleeve 13 is fused with the optical fibers 3, 3 by the heating and reinforcing device 2 (Japanese Patent No. 3337874 and Japanese Patent No. 3334426).
Prior to execution of the fusion splicing step with the optical fiber fusion splicing device 1, one of the optical fibers 3, 3 is inserted into the inner-tube 132 to attach the heat shrinkable reinforcing sleeve 13.
As shown in FIG. 1A, the heating and reinforcing device 2 is generally comprised of a housing 21 to house the fusion spliced optical fiber 3, a lid 22 mounted to the housing portion 21, and the heater (not shown). The lid 22 is attached to the housing portion 21 through a hinge mechanism or the like so as to be able to open and close. The fusion spliced optical fiber 3 is housed in a predetermined position in the housing 21 in a state where the lid 22 is open. When the lid 22 is closed, the inserted optical fiber 3 is held by the lid 22 to the predetermined position, and the heat shrinkable reinforcing sleeve 13 is heat shrunken by the heater (not shown) and the inner-tube 132 and the hot-melt 133 are fused at the fusion splicing point M of the optical fiber 3 and its vicinity (a heating step).
While heating the fusion spliced optical fiber 3 and the sleeve 13, because the strength member 134 is made of metal or the like and withstands an amount of heat generated by the heater, the strength member 134 is not melted and keeps its shape in the heat shrinkable reinforcing sleeve 13.
The strength member 134 is disposed in parallel with the fusion splicing point M of the fusion spliced optical fiber 3 and reinforces the fusion spliced optical fiber 3.
As a result of the above-heating step, the melted inner-tube 132 and hot-melt 133 fix the strength member 134 and the fusion splicing point M of the fusion spliced optical fiber 3, all of which are covered with the outer-tube 131.
In general, prior to carrying out the heating and reinforcing step, a mid point C3 of the heat shrinkable reinforcing sleeve 13 and the fusion splicing point M have to be aligned with each other. If the same tool (a sheath remover, cutter, or the like) is used to obtain a flat face at the pair of left and right optical fibers 3, 3, lead lengths of the left and right optical fibers 3, 3 from which the sheaths have been removed are the same as each other.
As shown in FIG. 1B, the total length (L1×2) of the lengths L1 of lead portions 31, 31 of the pair of left and right optical fibers 3, 3 are set to be shorter than a length L2 of the heat shrinkable reinforcing sleeve 13. Therefore, portions of the heat shrinkable reinforcing sleeve 13 are also fused over an overwrap portion 17, 17 of the sheaths of the left and right optical fibers 3, 3. If a length of the overwrap portion 17 is L3, length L3 can be obtained by (L2−L1×2)÷2. Therefore, L2=L3×2+L1×2 (FIG. 1B). If left and right optical fibers 3, 3 are subjected to heating and reinforcement, it is preferable that this relationship is satisfied.
Consequently, in order to satisfy this relationship, the fusion splicing point M of the optical fiber 3 and a mid point C3 of the heat shrinkable reinforcing sleeve 13, and a mid point C2 of the heating and reinforcing device 2 are aligned with one another while heating and reinforcing step.
If the heating and reinforcing step is carried out in a state where the points M, C2, and C3 not aligned with each other, the length L3 of the overwrap portion 17 will be short and therefore not all parts of the lead portions 31 (a bare fiber) may be heated and reinforced.
In this case, the strength of the fusion spliced optical fiber 3 is not sufficiently secured, a portion of the lead portions 31 is left exposed, the fusion splicing point M is not sufficiently protected, and the fusion spliced optical fiber 3 lacks reliability in communications.
Furthermore, heretofore, if air is left between the fusion spliced optical fiber 3 and the heat shrinkable reinforcing sleeve 13 while carrying out the heating and reinforcing step, the heat shrinkable reinforcing sleeve 13 and the fusion spliced optical fiber 3 or the overwrap portion 17 may peel off from each other, which causes strength and reliability problems and the like.
Therefore, in order to eliminate air remaining inside the heat shrinkable reinforcing sleeve 13, the heating and reinforcing step is gradually carried out from the mid point C2 toward end portions of the heating and reinforcing device 2 or a portion to be heated is sloped so that shrinkage occurs from the mid point C2 to opposite ends.
If the heating and reinforcing step is carried out in the case where the fusion splicing point M, the mid point C3 of the heat shrinkable reinforcing sleeve 13, and the mid point C2 of the heating and reinforcing device 2 are not aligned with each other, distances respectively from the mid point C2 of the heating and reinforcing device 2 where heating starts to the left and right opposite ends where the heating and reinforcing step ends are different from each other and time required to melt one heat shrinkable reinforcing sleeve and time required to melt the other sleeve 13 do not coincide with each other. As a result, bubbles may be trapped.
Therefore, it is important that the fusion splicing point M, the mid point C3 of the heat shrinkable reinforcing sleeve 13, and the mid point C2 of the heating and reinforcing device 2 are aligned with each other while carrying out the heating and reinforcing step. Hereafter, an operation for aligning the mid points as described above is referred to as a centering operation.
FIGS. 2A to 2C show a related art centering operation with the conventional heating and reinforcing device 2. One of optical fibers 3, 3 to be fusion spliced to each other is passed through the heat shrinkable reinforcing sleeve 13 in advance. After the fusion splicing step has finished, an operator O opens the optical fiber holder 11 and moves the fusion spliced optical fiber 3 to the heating and reinforcing device 2. As shown in FIG. 2A, at this time, the operator O lowers one side of the fusion spliced optical fiber 3 with respect to the other side (or lifts the one side with respect to the other side) and, as a result, the heat shrinkable reinforcing sleeve 13 slides along with the fusion spliced optical fiber 3 in a direction of an arrow in FIG. 2A due to its own weight. Here, the operator O manually lifts and lowers the fusion spliced optical fiber 3 to move the heat shrinkable reinforcing sleeve 13 to a state where the fusion splicing point M of the fusion spliced optical fiber 3 and the mid point C3 of the heat shrinkable reinforcing sleeve 13 are aligned with each other. Here, the operator O visually checks whether the mid point C3 and the fusion splicing point M are aligned with each other.
As shown in FIG. 2B, the operator O moves the fusion spliced optical fiber 3 together with the heat shrinkable reinforcing sleeve 13 to the mid point C2 of the heating and reinforcing device 2 while keeping the mid point C3 of the heat shrinkable reinforcing sleeve 13 and the fusion splicing point M are aligned with each other.
With reference to FIG. 2C, the operator O visually confirms that the fusion splicing point M, the mid point C3 of the heat shrinkable reinforcing sleeve 13, and the mid point C2 of the heating and reinforcing device 2 are aligned with each other. Then, the heat shrinkable reinforcing sleeve 13 and the fusion spliced optical fiber 3 are moved together into the housing 21 of the heating and reinforcing device 2. The lid 22 is closed and a heating and reinforcing step starts.
FIG. 3 shows another centering method with another related art heating and reinforcing device.
With reference to FIG. 3, to align the fusion splicing point M and the mid point C3 of the heat shrinkable reinforcing sleeve 13 to each other, the fusion spliced optical fiber 3 is slid in parallel with the heating and reinforcing device 2 and in a direction of an arrow in FIG. 3 while keeping the heat shrinkable reinforcing sleeve 13 in contact with a portion (designated by P in FIG. 3) of the heating and reinforcing device 2. After sliding the fusion spliced optical fiber 3 until the fusion splicing point M of the fusion spliced optical fiber 3 and the mid point C3 of the heating and reinforcing device 2 are aligned with each other, the operator O puts the optical fiber 3 together with the heat shrinkable reinforcing sleeve 13 in the mid point C2 of the heating and reinforcing device 2 similarly to the above description, and the heating and reinforcing step is executed.
FIG. 4 shows a related art recoater. The recoater 5 is one of the related art reinforcing devices. As a method of reinforcing the fusion splicing point M of the fusion spliced optical fiber 3, in addition to the above case of using the heating and reinforcing device 2 and the heat shrinkable reinforcing sleeve 13, there is a method in which special resin (UV curing resin) is injected into and around the fusion splicing point M of the recoater 5 and a light for curing the resin is irradiated to a portion where the resin has been injected to thereby coat the fusion splicing point M with the resin (Japanese Patent Application Laid-open No. 7-311316).
The recoater 5 is generally formed of a die mold 51 into which the fusion splicing point M is fixed and the resin is injected, a gate 52 formed on the die mold 51 and through which the UV curing resin is injected, a light irradiation portion (not shown), and holders 53, 53 for fixing the fusion spliced optical fiber 3.
The die mold 51 further comprises main bodies 51a, 51b detachable from each other.
The gate 52 may be provided to one of or each of the main bodies 51a, 51b in advance. End faces of the main bodies 51a, 51b to be joined to each other are provided with left and right inserting holes 54 into which the fusion spliced optical fiber 3 is inserted.
The gate 52 is provided to a center on the die mold 51 and the fusion splicing point M needs to be disposed precisely in a position of the gate 52 while executing a reinforcing step. In the centering operation using recoater 5, the operator O aligns the fusion splicing point M and the gate 52 with each other by a visual check similarly to the case using the heating and reinforcing device 2.
3. Problems With The Related Art
However, the centering operation is carried out by the visual check by the operator O in the above method with the fusion splicing device 1 and the heating and reinforcing device 2, especially the operation of aligning the mid point C3 of the heat shrinkable reinforcing sleeve 13 with the fusion splicing point M requires skill, and it is difficult to carry out precise centering. In this method, a deviation of about ±1 mm occurs in the conventional centering operation.
In lifting and lowering the opposite ends of the fusion spliced optical fiber 3 to allow the heat shrinkable reinforcing sleeve 13 to slide due to its own weight, the operator O has to change a position of the optical fiber 3 to hold over and over again. In this case, if the fusion spliced optical fiber 3 has only a short extra length to be connected and from a closure or a cable into which the fusion spliced optical fiber 3 is inserted, the operator O may forcibly pull out the fusion spliced optical fiber 3 so as to change the hold position and, as a result, may damage the sheath of the fusion spliced optical fiber 3 or break the fusion spliced optical fiber 3.
In this centering operation, because the heat shrinkable reinforcing sleeve 13 which has been housed in the heating and reinforcing device 2 is positioned in heating portion in the heating and reinforcing device 2, the fusion spliced optical fiber 3 extending out of the heating and reinforcing device 2 from the left and right surface of the device 2 is gradually pulled or pushed back to thereby position the fusion splicing point M of the fusion spliced optical fiber 3 to the mid point C3 of the heat shrinkable reinforcing sleeve 13 after the heat shrinkable reinforcing sleeve 13 has once being housed in the heating portion. In order to carry out the centering operation by this method, the fusion spliced optical fiber 3 needs to be reciprocated leftward and rightward many times and it is difficult to align the fusion splicing point M, the mid point C2 of the heating and reinforcing device 2, and the mid point C3 of the heat shrinkable reinforcing sleeve 13 with each other.
In the method in which the heat shrinkable reinforcing sleeve 13 is brought in contact with the end portion P of the conventional heating and reinforcing device 2, the end portion P of the conventional heating and reinforcing device 2 is not necessarily formed into a structure suitable for allowing the heat shrinkable reinforcing sleeve 13 to come in contact with the end portion P. Therefore, the centering operation is difficult, and besides, there is a fear of damaging the fusion spliced optical fiber 3 while sliding the fusion spliced optical fiber 3.
Additionally, according to the method with the recoater 5, a mid point C4 of the die mold 51 and the fusion splicing point M need to be aligned with each other and the operator O needs to constantly give consideration so as to position the fusion splicing point M at the mid point C4 of the die mold 51 while moving the fusion splicing point M and also after the fusion splicing point M is positioned to the die mold 51. The fusion spliced optical fiber 3 used in the recoater 5 has a sheath diameter of 250 to 900 μm in many cases and the visual centering has an extremely low efficiency and requires skill of the operator O.
Also, because a speed at which the UV curing resin is filled via the gate 52 into the die mold 51 is constant, the UV curing resin is not evenly filled, and besides, it takes longer to fill the resin if the mid point C4 and the fusion splicing point M are not aligned with each other.
Furthermore, in a state where the resin is not fully filled, pressure in the die mold 51 is uneven, and therefore it is difficult to obtain a uniform UV sheath diameter after UV cure.
The present invention has been made to solve the above-described problems of the related art methods, and it is an object of the invention to provide an optical fiber reinforcing method and an optical fiber reinforcing device in which a fusion splicing point of an optical fiber, a mid point of a heat shrinkable reinforcing sleeve, and a mid point of a heating and reinforcing device can easily be aligned with each other.